Scanner characteristic adjustment

ABSTRACT

A method and system sense print a calibration feature towards an edge of a medium, scan the feature to determine a parameter and adjust a characteristic of the scanner based on the parameter.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional application filed under 37C.F.R. 1.53(b) and claims priority from co-pending U.S. application Ser.No. 10/777,559 filed on Feb. 11, 2004 and entitled METHOD AND APPARATUSFOR GENERATING A CALIBRATION TARGET ON A MEDIUM by Eric L. Andersen andWesley Alan Fujii, the full disclosure of which is hereby incorporatedby reference.

BACKGROUND

Scanners have proven useful in allowing the electronic capture ofimages. Various types of scanners are known, including flatbed, drum,and handheld scanners. Some scanners include automatic document feedersto enable rapid and efficient scanning of multiple documents. Somecharacteristics of a scanner, however, are most useful whenappropriately calibrated. For example, scanning is most efficient when aregion scanned corresponds closely to an actual extent of the objectbeing scanned. Hence, it may be desirable to calibrate thecharacteristic corresponding to the lateral and longitudinal positioningof the scanning region relative the object being scanned.

For example, in a scanner with an automatic document feeder, the lateralposition or alignment of the document being scanned relative to the scanhead depends on mechanical tolerances in the document feeder and theposition of the scan head. The alignment may need to be calibrated atinitial manufacturing. Furthermore, the alignment can change with timedue to wear and drift of components or due to servicing of the scanner.Calibration of this alignment characteristic may therefore be desirable.

Similarly, longitudinal positioning can depend on the relative timing ofthe document edges (leading and/or trailing) passing the scanning head.For example, in an automatic document feeder, there may be a mediasensor separate from the scan head for triggering the start or end ofscanning. Often, the media sensor is a mechanical or photoelectricdetector. Timing between the media sensor and scan head may be dependenton the mechanical tolerances in the document feeder and thecharacteristics of the medium. For example, the rate at which media isfed through the document feeder will vary depending on mechanical wearand tolerances in the document feeder as well as the thickness, surfaceroughness, and other characteristics of the media. Calibration of thesetiming characteristics may also be desirable.

Hence, it is often desirable to perform calibration on a scanner tocorrect for positioning and timing errors.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is flow chart of a method of printing a calibration target inaccordance with an embodiment of the present invention;

FIG. 2 is an illustration of a calibration target after printing a firstcalibration feature in accordance with an embodiment of the presentinvention;

FIG. 3 is an illustration of a calibration target after printing asecond calibration feature in accordance with an embodiment of thepresent invention;

FIG. 4 is an illustration of a calibration target after printing asecond calibration feature in accordance with another embodiment of thepresent invention;

FIG. 5 is an illustration of a calibration target after printing a firstcalibration feature in accordance with another embodiment of the presentinvention;

FIG. 6 is an illustration of a calibration target after printing asecond calibration feature in accordance with another embodiment of thepresent invention;

FIG. 7 is an illustration of a calibration target after printing asecond calibration feature in accordance with another embodiment of thepresent invention;

FIG. 8 is flow chart of a method of calibrating a scanner using acalibration target in accordance with an embodiment of the presentinvention;

FIG. 9 is an illustration of the results for scanning a calibrationtarget similar to FIG. 3 in accordance with an embodiment of the presentinvention;

FIG. 10 is an illustration of the results for scanning a calibrationtarget similar to FIG. 7 in accordance with an embodiment of the presentinvention;

FIG. 11 is an illustration of the results for scanning a calibrationtarget similar to FIG. 4 in accordance with an embodiment of the presentinvention;

FIG. 12 is a simplified illustration with a cutaway internal view of aprinter capable of generating a calibration target in accordance with anembodiment of the present invention;

FIG. 13 is a simplified illustration with a cutaway internal view of ascanner capable of performing calibration using a calibration target inaccordance with an embodiment of the present invention;

FIG. 14 is flow chart of a method of generating a calibration targetusable for calibrating a medium edge dependent characteristic of ascanner in accordance with an embodiment of the present invention;

FIG. 15 is an illustration of a calibration target produced inaccordance with the method of FIG. 14 in accordance with an embodimentof the present invention;

FIG. 16 is an illustration of a calibration target produced inaccordance with the method of FIG. 14 in accordance with an embodimentof the present invention;

FIG. 17 is flow chart of a method of generating a calibration targetusable for calibrating a medium length dependant characteristic of ascanner in accordance with another embodiment of the present invention;

FIG. 18 is an illustration of a calibration target produced inaccordance with the method of FIG. 17 in accordance with an embodimentof the present invention;

FIG. 19 is an illustration of a calibration target produced inaccordance with the method of FIG. 17 in accordance with an embodimentof the present invention;

FIG. 20 is flow chart of a method of calibrating a scanner using acalibration target which includes a calibration feature extendingsubstantially to an edge of the calibration target in accordance with anembodiment of the present invention;

FIG. 21 is a simplified illustration of portions of a scanner showing ascan head and media sensor in accordance with an embodiment of thepresent invention;

FIG. 22 is a simplified illustration of portions of a laser printer thatincludes a media sensor in accordance with an embodiment of the presentinvention;

FIG. 23 is flow chart of a method of calibrating a medium lengthdependant characteristic of a scanner using a calibration targetcomprising a first and second calibration feature located at oppositeends of the calibration target in accordance with an embodiment of thepresent invention;

FIG. 24 is a timing diagram showing the timing of output from the mediasensor and scan head of FIG. 21 when the calibration target similar toFIG. 15 is fed and scanned; and

FIG. 25 is a timing diagram showing the output from scan head of FIG. 21when the calibration target similar to FIG. 18 is fed and scanned.

DETAILED DESCRIPTION

Reference will now be made to the exemplary embodiments illustrated inthe drawings, and specific language will be used herein to describe thesame. It will nevertheless be understood that no limitation of the scopeof the invention is thereby intended. Alterations and furthermodifications of the inventive features illustrated herein, andadditional applications of the principles of the inventions asillustrated herein, which would occur to one skilled in the relevant artand having possession of this disclosure, are to be considered withinthe scope of the invention.

A first embodiment of the present invention provides a method 10 ofprinting a calibration target on a medium. Such a calibration target maybe suitable for use in calibrating a scanner as shown in FIG. 1. Themethod includes inserting 12 the medium into the printer with a firstorientation. The method further includes printing 14 a first calibrationfeature on the medium at a first lateral location, a location that isoffset from the center of the medium. The method further includesreinserting 16 the medium into the printer with a second orientationrotated 180 degrees from the first orientation. The method furtherincludes printing 18 a second calibration feature on the medium at asecond lateral location. By reinserting the medium into the printerreoriented 180 degrees, offset introduced by the printer may appear in asubstantially symmetrically opposite manner on the first and secondcalibration features.

Some embodiments of the method may help reduce the effect of lateraloffset introduced by a printer. For example, in a laser printer, paperpath alignment from the input tray can vary by several millimeters (mm)and change over life as parts wear. Typical specifications for laserprinter accuracy in placement of an image on a page are plus or minus 5mm. However, it has been observed that page to page variations are muchsmaller, about 1 mm, corresponding to 24 pixels at 600 pixel per inch(PPI) resolution.

Some embodiments of the method may also help reduce the effect of errorsin a laser printer optical system. For example, laser printers aretypically most accurate near the centerline of the printed page due tolens shape and mirror alignment. Hence, by placing the calibrationfeatures near the centerline, a more accurate calibration target may beobtained.

FIGS. 2 and 3 illustrate an example application of the method 10 ofprinting a calibration target. FIG. 2 illustrates the medium 20 a afterprinting 14 a first calibration feature 22 on the medium. The laterallocation 24 of the first calibration feature on the medium will beoffset 26 relative to the centerline 28 of the medium. For example, ifthe first calibration feature is to be printed laterally centered on themedium, offset introduced by the printer will cause the firstcalibration feature to be slightly offset from center as illustrated inFIG. 2. Of course, it is not necessary for the calibration features tobe printed exactly at the center of the medium. If both the first andsecond calibration features are printed at the same nominal lateralposition, they will appear at substantially symmetric positions aboutthe centerline of the medium. The positions of the first and secondcalibration features may not be exactly symmetric due to page to pagevariations of the printer and other factors that will be apparent to oneof ordinary skill in the art. Furthermore, it is not necessary for boththe first and second calibration features to be printed at the samenominal position by the printer. If the first and second calibrationfeatures are printed at known, but different relative positions, thisknown difference can be taken into account in the calibration process,as discussed further below. Again, page to page variations of theprinter and other factors may result in small errors in the position ofthe first and second calibration features.

Optionally, an indicator 29, for example an arrow, may also be printedto aid in reinserting 16 the medium 20 a in the 180 degree rotatedorientation. For example, the indicator may be printed to point in adirection opposite to the orientation 38 the medium was originallyinserted into printer. Such an indicator would then show the 180 degreerotated orientation for reinsertion. Alternately, an indicator may alsobe printed to show the correct orientation of the target to be insertedinto a scanner to be calibrated.

FIG. 3 illustrates the medium 20 b after printing 16 a secondcalibration feature 32, where the medium has been rotated 180 degreesfrom the orientation of FIG. 2. The second calibration feature will alsobe offset 36 relative to the centerline of the medium, but in theopposite direction from the first calibration feature due to the180-degree rotation of the medium. The offsets 26, 36 will besubstantially identical. The offsets may not be exactly equal due topage to page variations of the printer and other factors that will beapparent to one of ordinary skill in the art.

Although the first and second calibration features 26,36 are illustratedin FIGS. 2 and 3 as wide, longitudinally oriented stripes, thecalibration features are not limited to stripes. The calibrationfeatures can be longitudinally oriented lines, groups of several lines,diagonal lines, shapes, patterns, dots, or other printed features aswill occur to one of ordinary skill of the art. Additionally, althoughthe first and second calibration features are shown in FIGS. 2 and 3 asoverlapping, the first and second calibration features may be printed ata nominal lateral position so there is no overlap, for example asillustrated in FIG. 7.

Printing of black calibration features on a white medium isadvantageous, due to the resulting high contrast. Other colors or graylevels may, however, also be used for the calibration features. Forexample, suitable contrast may be obtained using a mid-scale gray levelwhich may result in less toner or ink being used to print thecalibration target. Similarly, it may prove desirable to print on aparticular media type which is either colored or transparent to providefor calibration of a scanner to that particular media.

In an example embodiment, the printing of the first 22 and second 32calibration features is on the same face of the medium 20 b,accomplished by rotating the medium 180 degrees (that is, rotating themedium within a plane defined by the surface of the medium) asillustrated in the reorientation between FIGS. 2 and 3.

In an alternate embodiment, the printing of the first and secondcalibration features may be on opposite faces of the medium,accomplished by flipping the medium over a longitudinal edge asillustrated in the reorientation of medium between FIG. 2 and FIG. 4.FIG. 4 illustrates the medium 20 b after printing the second calibrationfeature 32 on the opposite side of the medium. The optional indicator 29on the hidden face of the medium is shown for clarity in FIG. 4,although it is to be understood that the indicator need not be printedexactly as illustrated.

In another embodiment of the present invention, more than onedirectional indicator 29 may be printed as illustrated in FIG. 5. In yetanother embodiment of the present invention, the directional indicatormay be located in such a way that the second calibration feature isprinted directly over the directional indicator as illustrated in FIG.6. In yet another embodiment of the present invention, a seconddirection indicator may be printed while printing the second calibrationfeature to show the correct direction for insertion of the target into ascanner.

Another embodiment of the present invention provides a method 80 ofcalibrating a scanner using a calibration target as shown in FIG. 8. Thecalibration target includes a first calibration feature at a firstlateral location and a second calibration feature at a second laterallocation, the first and second lateral locations are in a known relationto each other and may be offset by a printer offset. The method includesthe step of locating 82 a first position of the first calibrationfeature, wherein the first position is laterally offset from the centerof the medium. The method also includes the step of locating 84 a secondposition of the second calibration feature, wherein the second positionis laterally offset from the center of the medium in a directionopposite to the lateral offset of the first position. The method alsoincludes the step of adjusting 86 a lateral calibration characteristicbased on the first and second positions. Using this method, printeroffset may be compensated for. Lateral calibration characteristics mayinclude hardware or software adjustments within the scanner thatcorrectly define the center or edges of the page. Printer offset may becompensated for in that errors related to the printer offset may bereduced or even eliminated entirely during the step of adjusting.

Locating the first and second position will now be described in furtherdetail. FIGS. 9-11 show the results for scanning a calibration target.The horizontal axis represents the lateral position of a row of pixelsscanned by the scanning head. The vertical axis represents the pixelvalue. FIG. 9 represents the results for scanning a calibration targetsimilar to that illustrated in FIG. 3. FIG. 10 represents the resultsfor scanning a calibration target similar to that illustrated in FIG. 7,and FIG. 11 represents the results for scanning a calibration targetsimilar to that illustrated in FIG. 4.

With respect to FIG. 11, some further explanation is warranted.Referring to FIG. 4, since one calibration feature is located on theopposite side of the page, that calibration feature will be weaklyvisible to the scan head. Hence, the pixel value 112 of the feature onopposite side of the calibration target from the scanner head may bequite different from the pixel value 114 of the feature on the same sideof the calibration target as the scanner head. The difference in thepixel value corresponding to the features will depend on the degree oftransparency of the medium and any bleed through in the printingprocess. Of course, if a two headed scanner is used that scans bothsides of the calibration target simultaneously, the calibration featurescan be detected directly on each side, rather than relying on anytransparency or bleed through.

If a directional indicator (29, FIG. 2) is included, detection of thedirectional indicator may also be performed to ensure that thecalibration target was correctly inserted into the scanner. If thecalibration target is not correctly inserted a notification or promptmay be provided. Such notification may, for example, be provided by acomputer attached to the scanner or a display on a device that containsthe scanner.

Locating 82 the first position may be accomplished by finding the whiteto black (black to white) transition of the calibration features asshown by pixel a in FIGS. 9-11. Similarly, locating 84 the secondposition may be accomplished by finding the white to black transitionshown by pixel b.

Adjusting 86 a lateral calibration characteristic of the scanner mayconsist, for example, of determining a centerline position 62 within thescan head. For example, where the first and second calibration featuresare known to be located symmetrically opposite the centerline of themedium, the centerline position of the scanner may be chosen as thepixel exactly halfway between pixel a and b.

Alternately, as shown in FIG. 10, there may be more than one positionassociated with each calibration feature, in which case the samecalibration operation may be performed using either the outer edges (a,b), inner edges (a′, b′), or a combination of both.

Where the first and second calibration features are known to be locatedat different lateral positions, this may also be compensated for as willbe explained. Furthermore, the first and second calibration features arenot limited to longitudinally oriented features. In order to moreclearly explain how this is possible, a mathematical derivation will nowbe presented.

Calibration may be performed on a single row of pixels of lateralextent. Let x represent the nominal lateral position of the firstcalibration feature relative to the centerline of the medium where ithas intersected the scan head. Then −x+k represents the nominal lateralposition of the second calibration feature, where k is the knownrelative lateral position of the first and second calibration features.The first calibration feature will actually be printed on the medium ata lateral position of x+o, where o represents the printer offset. Thesecond calibration feature will actually be printed on the medium at alateral position of −x+k−o+e, where e presents the small page to pageerror of the printer.

The scanner will detect the first calibration feature at pixel positiona=x+o, and will detect the second calibration feature at pixel positionb=−x+k−o+e. If k is equal to zero, corresponding to the first and secondcalibration feature being printed at the same nominal lateral positions,the centerline pixel can be defined at the location equally between aand b. If k is some other, known, value, the centerline can be found byshifting point b by k (to yield b″=−x−o+e). In either case, the error indefining the centerline will be given by a+b−k, which yields an error ofe. The printer offset is thus substantially cancelled out with theexception of any remaining small page to page error e. As will beapparent to one skilled in the art, many other variations in coordinatesystems and selection of origins may be used in performing thiscalibration.

Note that, even if k varies along the longitudinal length of thecalibration target, for example when the calibration target is a slantedline, the centerline can still be found since k is known.

Although this derivation has focused on a single scan line, theinvention is not limited to using a single scan line. For example,calibration may be performed using multiple scan lines, for example, byaveraging the results for several scan lines.

Another embodiment of the present invention provides a method 140 ofgenerating a calibration target usable for calibrating a medium edgedependent characteristic of a scanner as shown in FIG. 14. A medium edgedependent characteristic may include time delay from a media sensor tothe scan head parameter in a scanner equipped with an automatic documentfeeder or definition of the beginning of scan location. The method 140allows a scanner to be calibrated to detect the edge of the medium. Themethod includes the step of inserting 142 the medium of a first mediumsize into a printer. The method further includes the step of configuring144 the printer to print for printing on a second medium size greaterthan the first medium size. The method further includes the step ofprinting 146 a first calibration feature extending past a normalprinting limit toward a first edge of the medium. A normal printinglimit is a location near the edge of a medium at which a printernormally will not print.

FIG. 15 provides an example calibration target 150 produced inaccordance with the method 140 just described. The calibration target isprinted on a first medium size, for example letter size paper (8.5×11inches). The printable area is usually limited to an area 152 within theedges of the medium and thus does not extend to the edge of the paper.By configuring the printer to print as if printing on a second mediumsize 154, for example, legal size paper (8.5×14 inches), the printingarea will be extended 156 past the edge of the paper. This enables theprinting of the first calibration feature 158 past the normal printinglimit (the boundary of area 152), into the extended printing area,toward the edge of the medium. The calibration feature may thus extendas far or as little into the extended printing area as desired. Forexample, the calibration feature may extend partway to the edge or allthe way to the edge, or past the edge of the medium. This allows ink ortoner to be placed as close to the edge as desired. For example, thefirst calibration feature 158 may be printed past the normal printingarea 152 up to, but not past, the edge of the medium as illustrated inFIG. 16. It is desirable, in some implementations, to place thecalibration feature close to the edge, for example within in a few scanlines, to provide the best accuracy with the calibration target. Byavoiding the placement of ink or toner off the page, this may helpprevent contamination of components within the printer by excess ink ortoner.

The first and second medium size are not limited to letter and legal,respectively. For example, the first medium size may be A4 size paper,and the second medium size may be legal size. Any second medium sizegreater than the first medium size in at least one dimension such thatthe extended printing area (for example, 156 in FIG. 15) is providedwill suffice. Various other combinations of paper sizes may be used,depending on the capability and configuration of the printer, as willoccur to one of ordinary skill in the art.

Another embodiment of the present invention provides a method 170 ofgenerating a calibration target usable for calibrating a medium lengthdependent characteristic of a scanner as illustrated in FIG. 17. Themethod 170 allows a scanner to be calibrated to detect the length of themedium. The method includes the steps 142, 144, 146 described for theprevious method 140. The method further includes the step of reinserting172 the medium into the printer at a second orientation reoriented by180 degrees from an original printing orientation. The method furtherincludes the step of printing 174 a second calibration feature on themedium extending past a normal printing limit toward an opposite edge ofthe medium so the second calibration feature extends toward the oppositeedge of the medium from the first calibration feature. A medium lengthdependent characteristic may include a rate of feeding through anautomatic document feeder, or a rate of movement of a scan head.

Although the method is not limited to any particular type of printer, wenow consider in further detail the operation of the method in a laserprinter that includes a media sensor. FIG. 22 illustrates a side view ofportions of a laser printer 220 that includes a feed 221, organic photoconductor 222, and media sensor 223. Media passes from the feed towardthe organic photo conductor (direction 224) which rotates (direction225) to transfer toner onto the medium at the transfer point 226. Thetoner is placed onto the organic photo conductor at the image formationpoint 227. Hence, it is desirable that the distance 228 from the imageformation point to the transfer point is less than the distance 229 fromthe media sensor to the transfer point. This helps to avoid the printerdetecting the trailing edge of the medium and disabling image formation.Hence, when using the method with an existing printer, it may beadvantageous to select a tray that has this property. Alternately,operation of the media sensor may be disabled while printing thecalibration target.

FIG. 18 provides an example calibration target 180 produced inaccordance with the method 170 just described. This shows thecalibration target after rotation by 180 degrees, hence the firstcalibration feature 158 is at the top of FIG. 18, and the secondcalibration feature 188 is near the bottom.

As discussed above, a directional indicator (e.g. 29 in FIGS. 2 and 16)may also be printed to aid in reinserting 172 the medium. Additionally,a directional indicator or other instructions may also be printed to aidin properly orienting and using the calibration target.

Although in some embodiments, it may be desirable that the first andsecond calibration features 158, 188 are printed on the same face of themedium, this is not necessary, as discussed previously. Furthermore, thefirst and second calibration features are not limited to rectangles asillustrated in FIGS. 15, 16, and 18; different shapes or patterns may beused as the calibration feature. Additionally, the lateral position ofthe calibration feature is similarly unconstrained, although it mayprove advantageous in some implementations to position the calibrationfeature(s) at a known lateral position. For example, if the calibrationfeature is placed at the same lateral location as the media sensor, thishelps to minimize errors introduced by skew in the media feed. Hence,the first and second calibration feature may be printed so that they areat approximately the same lateral position, for example as shown in FIG.18. Alternately, the first and second calibration feature may besymmetrically placed about a centerline of the media as previouslydiscussed.

Accordingly, in another embodiment of the present invention, acalibration target useful for simultaneous calibration of both alaterally sensitive characteristic and an edge sensitive characteristicof a scanner may be printed by printing the first calibration feature ata first lateral location and printing the second calibration feature ata second lateral location with a known relation to the first laterallocation. An example of such a calibration target 190 is shown in FIG.19.

Another embodiment of the present invention provides a method 200 ofcalibrating a scanner using a calibration target which includes acalibration feature extending substantially to an edge of thecalibration target as shown in FIG. 20. The method includes the step offeeding 202 the calibration target into the scanner. The method furtherincludes the step of determining 204 a parameter associated withscanning of the calibration feature. The method further includes thestep of adjusting 206 the medium edge dependent characteristic of thescanner based on the parameter relative to a reference value.

For example, the method 200 may be used to calibrate the time delay froma media sensor to the scan head parameter in a scanner equipped with anautomatic document feeder. FIG. 21 illustrates a side view of portionsof a scanner 210, with feed tray 212. Documents travel through the feed213 (direction 214) past a media sensor 215 to the scan head 216 andplaten 217. The time delay corresponds to the distance 218 from themedia sensor to the scan head.

FIG. 24 illustrates a timing diagram of the output 242 from the mediasensor (215 in FIG. 21) and the output 244 from the scan head (216 inFIG. 21) when a calibration target similar to that of FIG. 15 is fed andscanned. The horizontal axis represents time. As the calibration targetpasses the media sensor, the media sensor output will transition atreference time t₁. As the calibration target passes the scan head, thescan head output will transition at time t₂. Hence, the time delayparameter is given by t₁−t₂. This time delay parameter may be used toadjust the start scan timing of the scanner.

Another embodiment of the present invention provides a method 230 ofcalibrating a medium length dependant characteristic of a scanner usinga calibration target comprising a first and second calibration featurelocated at opposite ends of the calibration target and extended to edgesof the calibration target as shown in FIG. 23. The method 230 allows ascanner to be calibrated to detect the length of the medium. The methodincludes the step of feeding 232 the calibration target into thescanner. The method further includes the step of determining 234 a firstparameter associated with scanning of the first calibration feature bythe scanner. The method further includes determining 236 a secondparameter associated with scanning of the second calibration feature bythe scanner. The method further includes calculating 238 a medium lengthcalibration factor based on a difference between the first and secondparameter.

For example, FIG. 25 illustrates a timing diagram of the output 252 fromthe scan head (216 in FIG. 21) when a calibration target similar to FIG.18 is fed and scanned. The first transition at time t₁ corresponds tothe first parameter when the leading edge of the first calibrationfeature passes across the scan head. The last transition at time t₂corresponds to the second parameter when the trailing edge of the secondcalibration feature passes across the scan head. Hence, time t₁ and t₂correspond to the edges of the medium, or correspond to the mediumlength. A difference between t₁ and t₂ may be formed to provide a mediumlength calibration factor.

This medium length calibration factor may be used to adjustcharacteristics of the scanner operation that are dependent on mediumlength. For example, scan-line to scan-line placement will be a functionof the medium length calibration factor, or rate at which scanneddocuments feed past the scan head. Calibration to compensate for changesin medium length caused by mechanical wear, medium stretch or differingmedium surface characteristics can thus be accomplished. For example, byprinting a calibration target on the exact medium type to be scanned,inaccuracies due to differences in feed rate caused by the mediumsurface can be reduced. Similarly, periodic calibration for medium feedrate variations caused by mechanical wear may be conveniently performedby simply printing a calibration target and calibrating the scannerusing that calibration target.

Although described as though the scan head is fixed and the calibrationtarget moves across the scan head, those of ordinary skill in the artwill appreciate that the principle of operation is the same if thecalibration target is held in a fixed position on the scanner platen andthe scan head moves.

In accordance with another embodiment of the present invention, aprinter 120 capable of generating a calibration target on a medium isshown in FIG. 12. The printer may include a media feed 122, a printmechanism 124, and a first calibration target print mechanism 125. Theprint mechanism may be any device a printer can use to place ink ortoner on a medium, such as a revolving photoreceptor drum in a laserprinter (as shown in FIG. 12 124), a print head in an ink jet printer,and so forth. The first calibration target print mechanism may besoftware in a computer that is connected to a printer. The software cansend data to the printer instructing it to print a calibration target onthe medium. Alternatively, the first calibration target print mechanismmay be software, firmware, or hardware located in the printer that, whenactivated, allows a user to print a calibration target. The mechanismmay be activated by pushing a button on the printer.

In a first embodiment of the printer, the first calibration target printmechanism 125 is configured to cause the print mechanism 124 to print afirst calibration feature at a first lateral location on the medium.

In a second embodiment of the printer, the first calibration targetmechanism 125 is configured to cause the print mechanism 124 to print afirst calibration feature on the medium so that the first featureextends past a normal printing limit toward a first edge of the medium.

Optionally, in accordance with another embodiment of the presentinvention, the printer may include a medium reinsertion mechanism and asecond calibration target print mechanism 126. The medium reinsertionmechanism can be triggered by the first calibration target printmechanism 125 and configured to trigger reinsertion of the mediumreoriented by 180 degrees from an original orientation. In a thirdembodiment of the printer, the second calibration target print mechanismis configured to cause the print mechanism to print a second calibrationfeature at a second lateral location in known relation to the firstlateral location on the medium after reinsertion. In a fourth embodimentof the printer, the second calibration target print mechanism isconfigured to cause the print mechanism to print a second calibrationfeature on the medium after reinsertion so that the second calibrationfeature extends past a normal printing limit toward a second edge of themedium opposite the first edge.

Various options for the medium reinsertion mechanism will occur to oneof ordinary skill in the art. For example, in one embodiment, asillustrated in FIG. 12 the reinsertion mechanism may include a prompter128 which prompts a user to reinsert the medium into the printer. In analternate embodiment, the reinsertion mechanism may include a feed tray129, also known as a duplexing tray, which rotates the medium 180degrees from the original orientation. Alternately, the prompter 128 maybe provided by signaling a user through a computer attached to theprinter or a display on a device that contains the printer.

The details of the calibration feature(s) to be printed may be stored inan image file, or may be generated algorithmically. For example, animage file corresponding to the first calibration feature might bestored, and this same image file used to print the second calibrationfeature.

In accordance with another embodiment of the present invention, ascanner 130 capable of performing calibration using a calibration targetis shown in FIG. 13. The scanner includes a scan head 132, a locator 134communicating with the scan head, and an adjuster 136 communicating withthe scan head.

In a first embodiment of the scanner, the locator 134 is configured todetermine a first lateral feature parameter and a second lateral featureparameter, and the adjuster 136 is configured to accept the first andsecond lateral feature parameters from the locator and to determine alateral calibration characteristic based in part on the first and secondlateral feature parameters so that the printer offset is compensatedfor.

In a second embodiment of the scanner, the locator 134 is configured todetermine a parameter associated with the scanning of a firstcalibration feature, and the adjuster is configured to accept theparameter from the locator and to adjust a medium edge dependentcharacteristic of the scanner based on the parameter relative to areference.

In a third embodiment of the scanner, the locator 134 is configured todetermine a first parameter corresponding to the scanning of the firstcalibration feature and configured to determine a second parametercorresponding to the scanning of the second calibration feature, and theadjuster 136 is configured to accept the first and second parametersfrom the locator and to adjust a medium length sensitive characteristicof the scanner based on a difference between the first and secondparameters.

A calibration target produced in accordance with embodiments of theinvention can be printed on virtually any printer. Hence, a calibrationtarget can easily be printed by a customer or field service technicianusing a printer conveniently located near the scanner to be calibrated.This may reduce the expense and delay associated with special ordering acalibration target.

It is to be understood that the above-referenced arrangements areillustrative of the application for the principles of the presentinvention. Numerous modifications and alternative arrangements can bedevised without departing from the spirit and scope of the presentinvention. While the present invention has been shown in the drawingsand described above in connection with the exemplary embodiments of theinvention, it will be apparent to those of ordinary skill in the artthat numerous modifications can be made without departing from theprinciples and concepts of the invention as set forth in the claims.

1. A method comprising: inserting a medium of a first medium size into aprinter; configuring the printer for printing on a second medium sizegreater than the first medium size; and printing a first calibrationfeature extending past a printing limit associated with the first mediumsize toward a first edge; and scanning the first calibration feature;determining a parameter associated with scanning of the firstcalibration feature; adjusting a characteristic of the scanner based onthe parameter.
 2. The method of claim 1, wherein the parameter is afirst time associated with a passing of the calibration feature across ascan head and wherein the adjusting comprises adjusting an edgedependent characteristic of the scanner based on the parameter and areference value comprising a second time associated with a passing ofthe medium past a media sensor.
 3. The method of claim 1, furthercomprising the steps of: reinserting the medium into the printer at asecond orientation reoriented by 180 degrees from an original printingorientation; and printing a second calibration feature on the mediumextending past a normal printing limit toward an opposite edge of themedium so the second calibration feature extends toward a second edge ofthe medium opposite the first edge whereby the calibration target may beused to calibrate a medium length sensitive characteristic of thescanner.
 4. The method of claim 3, wherein the first calibration featureis printed at a first lateral location, and the second calibrationfeature is printed at a second lateral location with a known relation tothe first lateral location so that offset introduced by the printerappears in a substantially symmetrically opposite manner on the firstand second calibration features whereby the offset may be compensatedfor during use of the calibration target.
 5. The method of claim 3,comprising the step of printing a directional indicator showing thesecond orientation for reinsertion of the medium.
 6. The method of claim3, comprising the step of printing a direction indicator showing anorientation for insertion of the medium into a scanner.
 7. The method ofclaim 3, wherein the first and second calibration feature are printed ona same face of the medium.
 8. The method of claim 3, wherein the firstparameter is a first time corresponding to a beginning of the firstcalibration feature passing across a scan head and wherein the secondparameter is a second time corresponding to an end of the secondcalibration feature passing across the scan head.
 9. The method of claim3, wherein the first calibration feature is printed adjacent and up tothe first edge of the medium and wherein the second calibration featureis printed adjacent and up to the second edge of the medium.
 10. Themethod of claim 1, wherein the first calibration feature is printedadjacent and up to the first edge of the medium.
 11. A system,comprising: a printer comprising: a print mechanism configured to accepta medium; and a first calibration target print mechanism configured tocause the print mechanism to print a first calibration feature on themedium so that the first feature extends past a normal printing limit;and a scanner comprising: a scan head; a locator coupled to the scanhead and configured to determine a first parameter corresponding to thescanning of the first calibration feature; and an adjuster configured toaccept the first parameter from the locator and to adjust acharacteristic of the scanner based on at least partially upon the firstparameter.
 12. The system of claim 11, further comprising a mediumreinsertion mechanism coupled to the first calibration target mechanismand configured to trigger reinsertion of the medium into the media feedreoriented by 180 degrees from an original orientation; and a secondcalibration target print mechanism configured to cause the printmechanism to print a second calibration feature on the medium afterreinsertion so that the second calibration feature extends past a normalprinting limit toward a second edge of the medium opposite the firstedge, wherein the locator is configured to determine a second parametercorresponding to the scanning of the second calibration feature andwherein the adjuster is configured to accept the first parameter and thesecond parameter from the locator and to adjust a medium lengthdependant characteristic of the scanner based on a difference betweenthe first and second parameters.
 13. The system of claim 11, wherein themedium reinsertion mechanism comprises a prompter configured to promptreinsertion of the medium into the printer.
 14. The system of claim 11,wherein the medium reinsertion mechanism comprises a feed trayconfigured to rotate the medium 180 degrees from the originalorientation.
 15. The system of claim 11, wherein the first parameter isa first time corresponding to a beginning of the first calibrationfeature passing across a scan head and wherein the second parameter is asecond time corresponding to an end of the second calibration featurepassing across the scan head.
 16. The system of claim 11, wherein themedium length dependant characteristic is an adjustment for mediumstretch.
 17. The system of claim 11, wherein the medium length dependantcharacteristic is an adjustment for mechanical wear in a feed of thescanner.
 18. The system of claim 11, wherein the medium length dependantcharacteristic is an adjustment for medium surface characteristics. 19.A method comprising: inserting a medium of a first medium size into aprinter; printing a first calibration feature adjacent and up to a firstedge of the medium; and scanning the first calibration feature;determining a parameter associated with scanning of the firstcalibration feature; adjusting a characteristic of the scanner based onthe parameter.
 20. The method of claim 19, further comprising the stepsof: reinserting the medium into the printer at a second orientationreoriented by 180 degrees from an original printing orientation; andprinting a second calibration feature on the medium adjacent and up to asecond edge of the medium opposite the first edge of the medium, wherebythe calibration target may be used to calibrate a medium lengthsensitive characteristic of the scanner.